Aluminum alloys as a class are some of the most versatile engineering and construction materials available. For example, aluminum alloys are light in comparison to steel or copper and have high strength to weight ratios. Additionally, aluminum alloys resist corrosion, are up to three times more thermally conductive than steel, and can be easily fabricated into various forms. However, current commercial light-weight age-hardenable aluminum alloys are not useable above about 220° C. (428° F.) because the strengthening precipitates they contain dissolve, coarsen or transform to undesirable phases. Although aluminum-scandium alloys have been developed that can withstand higher temperatures, they are typically very expensive due to the costs associated with the use of scandium. Thus, there is a need for commercially viable uncladded aluminum alloys that have good processability characteristics and can be used in applications that are exposed to higher temperatures (e.g. 300-450° C. or 572-842° F.), such as automotive brake rotors or engine components. Cast iron, which is about three times heavier than aluminum, or titanium alloys, which are much more expensive than aluminum alloys, are commonly used for these high temperature, high stress applications.
Other potential applications for such aluminum superalloys include engine components such as pistons, where car manufacturers presently are limited to aluminum components that operate at a maximum temperature of about 220° C., therefore reducing engine efficiency, increasing emissions, and inflating the cost and mass of the cooling system. Another application is for aircraft engine structural components, such as the auxiliary power unit (APU) located in the tails of airplanes. APU frames, mounting brackets, and exhaust ducting currently use expensive titanium alloys due to the high-temperature environment of about 300° C. (572° F.), which could be replaced by lighter, much less expensive high-temperature aluminum alloys that are disclosed herein.
An inventive alloy, described herein in various embodiments, comprises aluminum, zirconium, and at least one inoculant, such as a Group 3A, 4A, and 5A metal or metalloid, and include one or more types of nanoscale Al3Zr precipitates. An alloy also can include aluminum, zirconium, a lanthanide series metal such as erbium and at least one inoculant, such as Group 3A, 4A, and 5A metals and metalloids. Such an alloy can have one or more nanoscale high number density precipitates such as Al3Zr, Al3Er, and Al3(Zr,Er) precipitates. The inventive alloy exhibits good strength, hardness, creep resistance and aging resistance at elevated temperatures and excellent electrical and thermal conductivity at all temperatures, while being less expensive than Sc-bearing aluminum alloys.